Electrical discharge tube



1 KAZUO TAKAYAMA ETAL 3,101,426

ELECTRICAL DISCHARGE TUBE File'd June 14, 1961 2 Sheets-Sheet 1 1963 KAZUO TAKAYAMA ETAL 3,101,426

ELECTRICAL DISCHARGE TUBE Filed June 14, 1961 2 Sheets-Sheet 2 GAS IKESSURE a 200 400 um DISCHARGE CUKKE N T NV (Alfons Kezuo Tau n l ama Su'jt' Ol'mn R 3' wajawl, C021. G/uu'udft 4 (.dJuu

fi'rl'onuaqs United States Patent Japan Filed June 14, 1961, Ser. No. 117,139 2 Claims. (Cl. 313-452) This invention relates to an electrical discharge tube.

Electrical discharge tubes are generally accompanied with electric oscillations and noises to greatly obstruct the practical use of such discharge tubes not only in general wireless instruments but also in precise experiments and measurements. For example, the flickers and noises in fluorescent lamps and the reduction of the S/N ratio of discharge tubes used in telephone circuits have all been caused by noises and oscillations during the discharge.

The conventional countermeasures against them have been used for the capacitance and inductance chiefly in the external circuits but have been so imperfect as to be powerless as preventive measures specifically against low frequency oscillations.

The present invention has been made by noting that the causes of such noises and oscillations in discharge tubes under the present circumstances are in the internal operating mechanism wherein the position of the boundary area between the space charge region and the plasma region of discharge in the discharge tube fluctuates with the slightest incentive. The perfect preventive measures are considered to be to stabilize such discharge mechanism.

An objectof the present invention is to provide an electrical discharge tube wherein noises and oscillations are prevented. 1

In the electrical discharge tube according to the present invention, a grid for preventing oscillations is provided in the vicinity of the boundary between the space charge region and the plasma region. 7

The invention is illustrated by way of example, in the accompanying drawings in which:

FIGURE 1 is a sectional view showing an embodiment of the electrical discharge tube according to the present invention;

FIGURE 2 is an elevation of a grid unit to be used in the discharge tube illustrated in FIGURE 1;

FIGURE 3 is a sectional view of another embodiment of the discharge tube according to the present invention;

FIGURE 4 is a perspective view of a grid unit to be used in the discharge tube illustrated in FIGURE 3;

FIGURE 5 is a characteristics diagram of the discharge tube illustrated in FIGURE 3.

With reference to the drawings, FIGURE 1 shows an embodiment of the discharge tube according to the present invention, which is of a fixed type adapted to be applied, for example, to fluorescent lamps. 1 is a lamp tube. 2 is an electrode. 3 is a grid unit. The grid unit 3 is provided with a grid 5 in a supporting frame 4. The position of the grid is mm. away from the electrode and the pitch of the grid is 4 mm.

The operation of the electrical discharge tube according to the present invention shall now be explained. As the gas pressure and discharge current in the fluorescent lamp are constant, if such grid as is illustrated in FIGURE 2 is provided in the discharge circuit so as to float near the boundary between the space charge region and the plasma region, the floating potential Vg will be determined by the potential distribution and electron temperature within the discharge tube. That is to say, if the potential in which the grid is placed is V,

Vg: V- V) (1) 3 ,101,426 Patented Aug. 20, 1963 "ice wherein k is Boltzmanns constant,

e is the charge of electrons,

Te is the temperature of electrons, Ti is the temperature of ions,

Me is the mass of electrons, and Mi is the mass of ions.

It is considered that, as Vf in the Formula 1 is always positive, a fixed potential Well will be formed in the position of the grid between the boundary surfaces of the space charge region and the intermediate plasma region where the oscillations of the discharge tube are caused, the instability of the position will be forcibly suppressed and the tube will be stabilized.

The grid may be made of a metal or an insulator. The pitch and size of the grid may be diiferent depending onthe respective applications. Such grid may totally or partially enclose the electrode. The grid may be electrically applied a proper potential with respect to the electrode but will be eflective enough only if it is left to float.

In case the grid is left to float, it will be effective to be used in the plasma in which not only electrons and ions coexist but also there are charged particles. That is to say, when the grid is placed therein, the charged particles will be deposited on the grid surface and the grid will be of a fixed potential different trom the potential in its vicinity. Under such circumstances, the same as in the case that a potential is applied on an ordinary grid, the discharge passage can be controlled.

Shown in FIGURES 3 and 4 is another embodiment of the discharge tube according to the present invention wherein the grid unit is movable. 6 is an enclosing tube. 7 is an directly heating type cathode. 8 is an anode. 9 is a grid unit. 10 is a sliding tube fitted with the grid unit 9. 11 is a grid. In this embodiment, the pitch of the grid is 2 mm. and the diameter of the grid is 30 mm. The sliding tube is made of nickel. The curvatures of the electrode 8 and grid unit 9 are so made as to conform to the potential distribution within the tube.

In this case, as the position of the grid can be varied by moving the sliding tube 10 with a magnet from outside, it is possible to place the grid in a position where oscillations can be most elfectively prevented. Therefore, such grid may be used in the case that the operating point of the discharge tube varies greatly.

FIGURE 5 shows a characteristics diagram by experiments wherein the distance between the grid and anode of the discharge tube illustrated in FIGURE 3 was 20 mm. and the enclosed gas was helium. This diagram shows the relation between the gas pressure (below 10 mv.) at whichoscillations stopped and the discharge current. as measured between the terminals. The hatched part represents a non-oscillation region. The region B enclosed by the curve T represents the case that the grid was kept in close contact with the anode and corresponds to the state wherein there wasno grid in effect. The region A +B enclosed by the 'curve II corresponds to the case that the grid was placed in a position 20 mm. away from the anode and shows that the non-oscillation region was expanded. Outside the hatched region, the oscillation voltage reached several volts to several tens of volts.

What is claimed is: r

1. An electrical discharge tube wherein a grid for preventing oscillations is provided in the vicinity of the boundary between the space charge region and the plasma region, which grid has a floating potential and is movable.

2. In a fluorescent lamp or the like, having an envelope containing a gaseous discharge maintained between two 3 electrodes, improvements for reducing oscillations incurred during the discharge, comprising in combination, a floating grid electrode means movably mounting the electrode in frictionally engaged position in the vicinity of the boundary between the space charge region and the plasma region act the tube, the grid including magnetic structure to permit movement of its position against the frictional engagement by force of -a magnetic field placed outside the envelope, whereby in view of the variations in structure of the tube or the variations of operating potentials at different locations which will change the locations of the space charge and plasma regions, the grid may be moved to the most effective position to reduce oscillations in each tube after construction.

References Cited in the file of this patent UNITED STATES PATENTS Gerber July 24, 1951 Mason Nov. 29, 1953 

1. AN ELECTRICAL DISCHARGE TUBE WHEREIN A GRID FOR PREVENTING OSCILLATIONS IS PROVIDED IN THE VICINITY OF THE BOUNDARY BETWEEN THE SPACE CHARGE REGION AND THE PLASMA REGION, WHICH GRID HAS A FLOATING POTENTIAL AND IS MOVABLE. 